Greenhouses are just one step in the continuum for protected cultivation. They just so happen to be at the top of the heap.
Let’s back up a bit.
Crops have been grown outside for thousands of years (perhaps 10,000 years, beginning in the Fertile Crescent, according to theories). But growing outside includes exposure to whatever perils nature throws at the field — torrential rains, parching droughts, scorching heat, and frigid cold, to name just a few Therefore, the concept of trying to protect the crop from some of the most extreme weather fluctuations was conceived.
Protected agriculture has many applications. However, the primary purpose is economic. If a producer can extend the growing season, even just a little earlier or a little later, the value
of the crop goes up.
The grower with the earliest tomatoes, peppers, lettuce, etc. is the one who rakes in the big bucks in those extra weeks of harvest. Likewise with end of season, and harvesting after the competition’s crops have bitten the frozen dust and turned to mush.
Check Out Your Options
We have a whole continuum of options for protecting our crops. Each allows the grower to shield the crop to some extent from extremes in temperature, light, or water, and perhaps offer some protection from insects, diseases, weeds, and air pollutants, as well.
Note that as we move up the ladder and get better protection, the cost of the materials and/or structure goes up sharply. However, the point of this article is that the returns go up even faster.
At the bottom end, mulching the crop is well-known to help with early season warming of the soil, resulting in faster growth of young transplants in early spring, and an earlier first harvest. The most common implementation is black polyethylene mulch, and we can see miles of these 3- to 5-foot-wide plastic ribbons on fields all over the world. It’s cheap, it works, and it brings in the early harvest premium.
Next, row covers, either supported with hoops or floating over the crop, give one more layer of protection. These can be used with or without mulch underneath, but the combination has been clearly shown to increase the benefits of either system alone. These are used worldwide, just like mulch.
The third step would be high tunnels. These are tall enough to walk inside of, and sure look a lot like greenhouses. But they have no utilities, which means no fans, no heat, and no lights.
Sometimes referred to as the “poor man’s greenhouse,” they have found a growing niche with vegetable growers in the U.S. and many other countries. These inexpensive structures can be used for extra-early or extra-late season vegetable, fruit, or flower production. They give more protection than mulch or row covers, and even longer periods of harvest, with resulting better returns. We are seeing more and more of these around the country.
And of course the fourth and top step of the ladder is the bona fide greenhouse. Complete with a heating system, some type of active or passive ventilation, automated fertigation, and often shade cloth and horizontal air flow fans, they provide the best chance for making the environment optimum for vegetable production.
The season extension capabilities are so good that in many parts of the country they are used year-round. This is the Cadillac of protected culture, costs far more than the other systems, but helps producers grow the highest value crops when they cannot be grown outside in the same area. Locally grown vegetables in the winter — that’s what it’s all about.
Back in the Fertile Crescent days, early forms of wheat, barley, flax, peas, lentils, vetch, and chickpeas were the main crops planted in the field. Although important crops even today, compared to modern day horticultural crops, these are very low value on a per acre basis. They are not suitable for greenhouses, row covers, or even mulch.
As you go up the protected culture ladder, the value of the crops selected should go up as well. Vegetable crops are a perfect choice for every rung — their value can be magnified with each step of the continuum. Which season extender will you use next season?